Planographic printing element having carboxylic acid treated image areas

ABSTRACT

A PLANOGRAPHIC PRINTING PLATE IS PROVIDED HAVING IMAGE AREAS FORMED BY TREATMENT WITH A CARBOXYLIC ACID AS A MARKING INK, THE ACID HAVING FROM ABOUT 12 CARBON ATOMS TO ABOUT 22 CARBON ATOMS. THE PLATE IS PREFERABLY A PAPERBASED, ELECTROPHOTOSENSITIVE SHEET BUT CAN COMPRISE OTHER BACKING MEMBERS AND OTHER IMAGE-RECEPTIVE PRINTING SURFACES.

United States Patent O 3,690,878 PLANOGRAPHIC PRINTING ELEMENT HAVINGCARBOXYLIC ACID TREATED IMAGE AREAS William H. Tandy, Mentor, Ohio,assignor to Addressograph-Multigraph Corporation, Cleveland, Ohio NoDrawing. Filed Jan. 9, 1970, Ser. No. 1,887 Int. Cl. (203g /00, 13/00US. CI. 96-13 11 Claims ABSTRACT OF THE DISCLOSURE A planographicprinting plate is provided having image areas formed by treatment with acarboxylic acid as a marking ink, the acid having from about 12 carbonatoms to about 22 carbon atoms. The plate is preferably a paperbased,electrophotosensitive sheet but can comprise other backing members andother image-receptive printing surfaces.

BACKGROUND OF THE INVENTION In planographic printing, that is, printingfrom a plane surface, the plate must readily accept a Water-repellent,ink-receptive image which is then tenaciously held by the plate. Thenon-image areas must be readily wetted by and retain a -1film of theaqueous lithographic solutions while rejecting the printing ink.

[Metal masters have been partially supplanted by nonmetallic carriersheets coated with a film capable of accepting and holding an oleophilicimage, or having an area chemically transformed into an ink receptiveimage area.

Lithographic ink is a grease type, and the master coatings will acceptlithographic ink. But if areas of the coating are covered withhydrophobic material such as typewriter ink, crayons, etc., and then theentire master surface treated with a conversion solution, the coveredareas are not converted.

Phosphate acids are used, for example, to convert the zinc oxide coatedplates to a hydrophilic oleophobic condition. The covered areas remainoleophilic. These areas will pick up lithographic ink and transfer inkreplicas of the image in the lithographic printing technique.

Sometimes it is desired to ad image areas to a master after it isprepared. For example, it is common practice to print masters ofcommonly used forms. A pen is used to apply a protective coating ofimaging ink to create an image for data which must be added to apre-printed planographic master, such as order numbers, shippingweights, addresses of receivers, etc., so that a suitable number ofduplicate copies can then be printed for distribution to those involved.This type of planographic master is relatively rough and porous ascompared to other types of masters. Prior to this invention, availableimaging inks have been susceptible to the penetration and running of theimaging ink beyond the edges of the actual printing areas. Existingimaging inks quickly penetrate the porous surface of direct-imageplanographic masters, leaving no oleophilic film in the image areas toaccept the lithographic ink. Moreover, in some cases, pen tips used indirect imaging scratch the surface of the plate, thereby facilitatingpenetration of the lithographic solution and accelerating its spreadinto the plate.

It would therefore, advance the art if a marking ink were developedwhich was capable of forming ink-receptive image areas on planographicmasters which held fast and resisted penetration of and spreading by theimaging ink.

SUMMARY OF THE INVENTION In accordance with the present invention, theimage areas of a planographic printing element are formed by contactwith a marking ink comprising carboxylic acid having from about 12carbon atoms to about 22 carbon atoms.

The preferred embodiment comprises a base sheet, preferably a paper baseresin coated to provide wet strength, and a water insoluble,film-forming coating overlying and adhered to the base sheet. Thecoating comprises photoconductive material, such as zinc oxide bonded tothe base sheet, to provide a plate, especially an electrostatic plate.The carboxylic acid reacts with the zinc oxide to form a securelybonded, oleophilic film comprising the water insoluble, ink receptivezinc salt of the acid. In this case the zinc oxide is naturally inkreceptive, and the usual practice has been to apply an oil base markingfluid to prevent later application of conversion solution from reachingthe naturally ink receptive image. However, typical base marking fluidsdo gradually soak into the supporting base and expose the zinc oxide.The zinc oxide is gradually converted by fountain solution, withresultant shortened image life. This invention operates on the premiseof converting the zinc oxide to a more resistant zinc salt, usually of afatty acid. The surface around the image is thereafter converted to ahydrophilic phosphate without affecting the image. The resistant Zincsalt remains as a master image for the life of a paper-based sheet whenused as on an offset duplicator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred backing member orbase sheet of a planographic master used in accordance with the presentinvention is paper, such as kraft paper, because of its relative lowcost, strength, and desired flexibiilty. The paper may weigh from about15 to 40 pounds per thousand square feet and be suitably resin treatedto provide additional strength, especially wet strength, with suchresins as ureaformaldehyde, melamine-formaldehyde, and the like. Thepaper may also be conventionally sized if desired.

Other base sheets can also be used. For example, the base may comprisecellulosic material, such as cellophane or cellulose acetate. 01', thebase can be metallic, preferably in foil form, and comprise such metalsas aluminum, copper or brass. Still further, although not as desirable,the base sheet can be relatively inflexible, such as a glass or micasheet.

In the preferred form, the water insoluble, film-forming coating whichoverlies the base sheet comprises a phootconductive zinc oxide. However,almost any photo-- conductor having sufiiciently high value of surfacephotoconductivity may be used in the coating, for example, anthracene,the photoconductive oxides, sulfides, selenides, tellurides and iodidesof cadmium, mercury, antimony, bismuth, thallium, molybdenum, lead orzinc, especially when chemically reactive with the carboxylic acid used.The manner of preparing a base sheet having a coating of photoconductivematerial is well known in the art. US. Pat. Nos. 2,993,787 to Sugarmanand 3,010,884 to Johnson et al., for example, described the preparationof such plates. In general, the zinc oxide or equivalent is mixed with afilm-forming resinous vehicle, such as polyvinyl alcohol, and a solvent,and then coated by conventional means on the selected backing. Afterdrying, the master is then cut or punched to a desired shape and size.

In place of the polyvinyl alcohol, other materials may be used such ashydroxyethyl cellulose, carboxymethyl cellulose, gum arabic, guar gum,and the like. Such a film-forming vehicle must beelectrically-insulating and is applied with the photoconductive materialfrom a suitable liquid medium, such as an aqueous dispersion. As a rule,the amount of photoconductor material used may range from about parts to900 parts per 100 parts by weight of the film-forming vehicle. Aplasticizer may be used with the vehicle to vary the physical propertiesof the final coating.

However, the coating forming the image receptive printing surface neednot be of the photoconductive type. The present invention alsocontemplates a planographic master having a coating comprising a finelydivided filler or pigment material and an adhesive hydrophilic colloidwhich serves as a binder. These masters are often referred to as directimage masters. The filler may comprise clay, such as Georgia clay orkaolin, blanc fixe, calcium sulfate, talc, titanium dioxide, and otherequivalent finely divided mineral pigments. The hydrophilic colloid maybe any of a large number of colloidal materials. In some cases, acolloid hardening agent may be used, such as formaldehyde. Exemplarycolloids include: gums such as arabic, mesquite, karaya, locust bean,guar, and the various alginates such as sodium alginate and ammoniumalginate; proteins such as casein, soya bean, zein, animal glue, gelatinand egg and blood albumin; still other hydrophilic colloidal materialssuch as starch, dextrin, pectins and derivatives thereof includingfibrous sodium pectate; and synthetic hydrophilic colloidal materials,such as carboxymethyl cellulose, sodium polyacrylate, methyl cellulose,hydroxyethyl cellulose, and polyvinyl alcohol. The hydrophilic colloidis used in an amount of about 15 parts to about 30 parts per 100 partsby weight of the filler or pigment, and the mixture applied from asuitable liquid carrier such as an aqueous dispersion.

Whether applied with an electroconductive material or a pigment colloidadmixture, the base sheet of the present planographic master may becoated by any convenient method. For example, the coating may be sprayedon or flowed on, or the base sheet may be dipped into the mixtures.Following the coating step, the assembly is dried. The dryingtemperature is not critical, but it should be sufficiently high toevaporate the liquid carrier but not so high as to burn or char thebacking or constituents of the coating.

The coatings may be of any convenient thickness. In flexible embodimentsof the invention, a paper backing, for example, may weigh from about 15to about 40 pounds per one thousand square feet. A layer of thephotoconductive material may have a thickness of about 0.3 to about 2.0mils, with a coating of about 0.5 mil in thickness being preferred. Asuitable weight of pigmented colloid coating may be from about 3 toabout pounds per side (more than one side can be coated) per onethousand square feet of base sheet. The laminated assembly is cut intosheets of suitable size to be used as plates in duplicating or otherplanographic printing machines.

Carboxylic acids useful in accordance with the present invention arethose having from about 12 carbon atoms to about 22 carbon atoms.Carboxylic acids having less carbon atoms tend to have sufficient watersolubility to be unsuited for the purpose intended. Carboxylic acidshaving more carbon atoms have too high molecular weights to be easilyand conveniently employed. Within the range indicated, both saturatedand unsaturated acids are contemplated, as well as both monocarboxylicand dicarboxylic acids, although monocarboxylic acids are preferable.The predominantly greasy acids are desired. Oleic acid is preferred,although stearic and isostearic acids provide excellent results.Isostearic acid is preferred to staric acid, since isostearic acid isliquid at room temperatures. Highly acceptable results are also obtainedwith eurcic and linoleic acids. Mixtures of acids may also be used.

The acid may be applied to a planographic master in any convenient form.Usually an organic solvent medium is used such as methylethyl ketone,carbon tetrachloride, naphtha, etc., and especially aromatic solventssuch as toluene, xylene, benzene, and benzaldehyde. Mixtures of solventscan also be used. The amount of acid dissolved in the organic solvent isnot at all critical, since the purpose is merely to apply some of theacid onto a plate.

Solvents or diluents are preferably used in an amount to give desiredflow properties for a specific pen or for other means by which the acidsolution is applied. In general, the acid may comprise from about 25percent to about 75 percent by weight of the solution. If desired forlegibility, easy proofreading, or a lingering record if the master isnot to be used immediately, the solution can also contain a waterinsoluble dye such as indulin, nigrosine (Nubian Resin Black availablefrom Allied Chemical and Dye Corporation) and the like. A black or darkblue dye is preferred for legibility.

The application of the acid-organic solvent mixture, which is in thenature of a marking ink, can be carried out by any tool capable ofdepositing the solution as desired onto a plate. Any relatively sharppointed instrument can be used for this purpose, such as a stylus, fibertipped pens, dip pens, ball point pens, rubber stamps, etc.

The carboxylic acid does not run on the plate, but, to the contrary,acts as a fixative. When a photoconductive material reactive with themarking ink is used, such as zinc oxide, the reaction is between thezinc oxide and the carboxylic group of the acid to form a permanent,chemically-bonded, water insoluble, oleophilic image consistingessentially of the zinc salt of the acid or acids used. When the inkreceptive, image reproducing surface comprises a pigment-hydrophiliccolloid combination, the marking ink sticks to the area to which it isapplied, probably by a mechanical, physical adhesive bond, althoughthere may well be other forces not readily understood which contributeto the desired result.

The following examples are intended to illustrate the invention andshould not be construed as limiting the claims.

Example 1 A mixture of the following compositions was prepared:Ingredient: Amount Polyvinyl alcohol grams 5 Methanol ml 60 Distilledwater ml 40 Photoconductive zinc oxide grams The polyvinyl alcohol wasdissolved in a mixture of the water and methanol, after which the zincoxide was dispersed in the mixture by blending for five minutes on ahigh speed blender. The blended mixture was then coated on a paperbacking to a thickness to provide a final dry coating of about 0.5 milin thickness. The coat- 1ng was then dried and the assembly cut orpunched to a desired shape and size. The product was anelectrophotographic recording element especially adapted for use inelectrostatic printing.

A marking ink was then prepared by admixing the ingredients of thefollowing formula:

Ingredient: Weight percent Oleic acid 65 Toluene 25 Nigrosine base dye10 By means of a stylus, some of the marking ink was applied in directimaging over an area of the electrostatic master initially prepared.Wherever the marking ink touched the plate, a deposit of zinc oleateformed even at room temperatures. When the resulting plate was attachedto and operated on a conventional duplicating ma chine, the zinc oleateremained chemically bonded to the plaltle, did not run, and reproducedthe image exceptionally we Example 2 A coating composition was preparedby first mixing together 640 grams of photoconductive zinc oxide, 533grams of a 30 percent solution of 30:70 copolymer butadiene and styrenein toluene, and 353 grams of acetone. The mixture was ball milled forabout eight hours. The resulting slurry or suspension was thick andviscous but flowed readily and could be spread with a coating knife toform a smooth, uniform coating. The suspension was coated on a cleansurface of thin aluminum foil and the solvent removed by evaporation toprovide a smooth, uniform dried coating of about 0.8 mil in thickness.The resulting sheet was flexible, and the coating remained bonded to themetal.

A marking ink was then prepared by admixing the following ingredients.

Ingredient: Weight percent Isostearic acid 43.4 Benzaldehyde 30 Toluene16.6 Nigrosine base dye When a dip pen transferred some of the markingink onto the plate initially prepared, an ink reproducing area formedconsisting essentially of zinc isostearate which ran well without toningin the non-image areas of an offset printing machine.

Example 3 Example 4 A wet strength paper was coated with a layercontaining parts of casein, 10 parts of gum arabic, 100 parts of clay,and parts of a 40 percent aqueous formaldehyde solution, all by weight.The paper was then dried and calendered.

A solution of mixed carboxylic acids was prepared consisting essentiallyof the following:

Ingredient: Weight percent Linoleic acid 20.1 Oleic acid 22.3 Stearicacid 1.0 Benzaldehyde Toluene 16.6 Nigrosine base dye 10 This markingink was applied by a pen to the planographic printing element firstprepared and found to provide image areas which also held fast, did notpermit excessive penetration by a printing ink, and reproduced well.

The present invention makes possible the addition of handwritten ortypewritten information to planographic masters for later duplication,especially such addition to the various direct image masters includingthose of the photoconductive type, such as a zinc oxide electrostaticmaster. It is unexpected that the defined carboxylic acids would be soeasily suitable for this purpose and particularly that the acids wouldreact at room temperatures with a photoconductive metal compound likezinc oxide.

Although the foregoing describes several embodiments of the presentinvention, it is understood that the invention may be practiced in stillother forms within the scope of the following claims.

What is claimed is:

1. A planographic printing plate prepared for printing comprising a basesheet, a layer of a water-insoluble, film-forming material coating thebase sheet selected from the group consisting of a photoconductivematerial, and an ink-receptive, image reproducing area on said layerformed by treating said area with a carboxylic acid having from about 12carbon atoms to about 22 carbon atoms.

2. In a process for preparing for printing a planographic printing platecomprising a base sheet and a layer of a water-insoluble, film-formingmaterial overlying the base sheet; the improvements comprising formingsaid film-forming layer from a material selected from the groupconsisting of a photoconductive material, and contacting a portion ofsaid layer with a carboxylic acid having from about 12 carbon atoms toabout 22 carbon atoms to form an ink-receptive, image reproducing areafrom said portion.

3. An electrostatic master prepared for printing comprising a basesheet, a layer of a water-insoluble, filmforming material coating thebase sheet comprising a metal-containing photoconductive material, anink-receptive, electrostatically produced first image area of saidlayer, and an ink-receptive, chemically-produced second image area ofsaid layer comprising the reaction product of said metal-containingphotoconductive material and a carboxylic acid having from about 12carbon atoms to about 22 carbon atoms.

4. The electrostatic master of claim 3 wherein said photoconductivematerial comprises photoconductive zinc oxide, and said second imagearea comprises an oleophilic zinc salt of said carboxylic acid.

5. The electrostatic master of claim 3 wherein said carboxylic acidincludes saturated and unsaturated carboxylic acids having from about 12carbon atoms to about 22 carbon atoms.

6. The electrostatic master of claim 3 wherein said carboxylic acidincludes monocarboxylic and dicarboxylic acids having from about 12carbon atoms to about 22 carbon atoms.

7. A process for preparing for printing an electrostatic mastercomprising a base sheet and a layer of a waterinsoluble, film-formingmaterial overlying the base sheet comprising a metal-containingphotoconductive material, said process comprising electrostaticallyproducing one image area on said layer, and chemically producing anotherimage area on said layer by contacting the metalcontainingphotoconductive material of said another image area with a carboxylicacid having from about 12 carbon atoms to about 22 carbon atoms.

8. The process of claim 7 wherein contacting said second image area withsaid carboxylic acid comprises reacting the metal of saidphotoconductive material with said acid.

9. The process of claim 7 wherein said photoconductive material containsphotoconductive zinc oxide, and contacting said second image area withsaid carboxylic acid forms an oleophilic zinc salt of said carboxylicacid.

10. The process of claim 7 wherein said carboxylic acid includessaturated and unsaturated carboxylic acids having from about 12 carbonatoms to about 22 carbon atoms.

11. The process of claim 7 wherein said carboxylic acid includesmonocarboxylic and dicarboxylic acids having from about 12 carbon atomsto about 22 carbon atoms.

References Cited UNITED STATES PATENTS 437,780 10/ 1890 Higgins 10627 X2,357,809 9/ 1944 Carlson 96l.5 X 2,427,921 9/1947 Pfaelzer 10627 X2,624,652 1/ 1953 Carlson 96-1 X 683,161 9/1901 White et al. 10614.52,138,836 12/1938 Brower 10627 X OTHER REFERENCES Carman: Theory of thePrinting of Lithographic Inks Part II, American Ink Maker, March 1950,pp. 36-38 and 65.

GEORGE F. LESMES, Primary Examiner J. R. MH.LER, Assistant Examiner US.Cl. X.R.

96-15; l01--460, 466, Digest 13

